Cost Per Impression vs. CPM: Understanding Advertising Metrics

If you are new to media buying, the terminology can be confusing. Two of the most common metrics you will encounter are Cost Per Impression (CPI) and Cost Per Mille (CPM). While they measure the same fundamental action—an ad being displayed on a screen—they evaluate it at completely different scales.

What is the Difference?

The distinction is purely a matter of volume:

• Cost Per Impression: The fractional monetary cost of a single ad load.
• CPM (Cost Per Mille): The standardized cost of 1,000 ad loads. ("Mille" is Latin for thousand).

Because the cost of a single impression is usually a tiny fraction of a cent (e.g., $0.002), the advertising industry uses CPM to make pricing easier to read, negotiate, and forecast.

How to Calculate Cost Per 1000 Impressions (CPM)

If you know your total spend and total views, you can easily determine your CPM rate. First, find the single impression cost, then multiply it by one thousand.

CPM Formula: (Total Cost ÷ Total Impressions) × 1,000

For example, if you spend $200 to generate 40,000 views:
($200 ÷ 40,000) = $0.005 per individual impression.
$0.005 × 1,000 = $5.00 CPM.

Converting Between the Two Metrics

If an advertising platform charges a flat CPM rate and you want to know the micro-cost, simply divide the CPM by 1,000. A $15.00 CPM equals $0.015 per individual impression. You can toggle between these two scales instantly using our dynamic cpm cost calculator, which displays both single-view and thousand-view pricing side-by-side.